When the ice thaws off our midwestern water gardens, it is simply a wonderful time of the year. Things are warming up and everything starts to grow again. How did our Koi and goldfish survive the winter? If we had done a proper job of leaf cleanup in the fall and maintained some circulation in the pond to keep a hole open, then our fish should be fine.
Wow, it is discovered that all of your fish that you’ve had for many years are gone! Not even any fish carcasses are found! What possibly could have happened? The raccoons that raided our bird feeders last fall and winter must have eaten them. What else could it be because we have not seen any other kind of critter around?
More than likely the animal responsible was a mink. They can slip in and out through the ice layer by way of the hole that is maintained. They can do this silently, take a fish, and then slip out without leaving any obvious evidence that it was there. At one time, there may have been a few scales or some mink tracks left behind but if you do not suspect a problem, why would you look for evidence?
These water wolves of our water gardens can be devastating for our clients especially the ones that view their fish as part of the “family.” It is amazing how often I have seen the evidence of mink predation and the client thinking that their fish are just hiding. These little critters are silent killers leaving very little evidence so it is tough to know they have a problem until it is too late to do anything.
Almost without fail, most water gardeners do not know that mink are present in their area. This combined with the fact that they are nocturnal, that is, being active primarily at night – they will not be seen or even suspected. Occasionally, mink may be active with some daylight but it is still difficult to detect them because they are small and move swiftly.
They can kill and eat the largest of our fish as well as the smallest. They are very efficient swimmers that can stay underwater for several minutes – even cold water. When it is cold, mink are the most efficient killers because the fish are lethargic due to the lower water temperatures. Whereas the mink are warm-blooded and can swim relatively fast to catch a fish. During the summer, it is a different story. The exact opposite is true and most fish can escape their jaws especially when “structure” is added to the pond.
The best structure is of the type that the fish can hide in, behind or under. A good example is black plastic storage crates that also serve a dual purpose to hold plant pots up off the bottom. Larger fish may need something else like plastic barrels that have been cut in half or have large enough holes cut in them so the fish can swim in and out easily. Structure may also be created with rockwork or underwater caves can be purchased (ex. Koi Kastles). The point is to provide something that the fish can escape from the mink’s teeth.
Mink occur over almost the entire United States and Canada with the exception of the desert southwest and tundra areas. A mink’s basic habitat requirement is a suitable permanent water area. So, water gardens that are within a mile or two of naturally occurring water, like a creek or lake, are more susceptible to having mink predation. However, there are instances where a wandering mink will find a pond further away. If a creek is within a stone’s throw of a client’s water garden and not in the desert southwest there is a very good chance that a mink will show up sooner or later.
There are a few things to look for to determine if a mink is preying on a water garden’s fish. If the fish are large that are being eaten, then scales will be evident. The mink has to drag the fish out of the water to eat it and in this process, scales will be left behind. There may be some fish parts left over but do not count on this. Mink track may be in the snow or mud. It is possible that their wet footprints will be left behind in the morning on the rocks or some hard surface but check for these in early morning before the tracks evaporate. Remember, nothing else will be disturbed around the pond. A raccoon will leave all kinds of disturbance, in most situations, especially if all the fish have been taken. One last thing to look for is how easily the fish are spooked. If they seem agitated then there is a good chance that a predator has been after them.
To stop mink predation you have to react immediately otherwise by the time you have rounded up the necessary tools to deter mink it may be too late for the rest of the fish. So, I always recommend to dye the water black the DAY you suspect a mink problem. This means either the pond owner needs to have some dye on hand or you need to have it on hand for your clients. For pond owners that I feel are vulnerable to mink, or even some other predator, I always advise them to stock the stuff. If they depend on me having the dye and they cannot get in touch with me immediately could spell certain death for more fish the next night. Once mink find a good source of food, they will be back in successive nights until the food source is gone.
I like to use black because it is the darkest. If the mink cannot see their prey then the fish are safe. Dyes made for water gardens will dissipate in time and do absolutely no harm to the ecosystem.
There are not very many good easy solutions for the pond owner that has had a mink show up. After the water is dyed then the next choices are to keep a large dog that has free run of the water garden area 24 hours a day. Keeping inexpensive fish is an option for the future but that is not really a choice at this point. If the pond is covered with ice, except for the circulation hole, then cover it with 1/2 to 1 inch hardware cloth or welded wire. Another alternative is to use a 12 inch high electric mesh fence for a month or so.
The best solution, in my view, is to remove the critter that is eating the fish. Trapping may not be what you can do or would prefer not to do but it WILL work. Contact the local DNR to make sure that you can legally do this. A pest control person/trapper may be able to help if you do not have the expertise.
Of all the critters that can prey on fish in our ponds, mink are the most difficult to detect and to deter. Knowing that they are around and that they can be a predator is the first step in solving the problem. If there is the possibility of having a water wolf problem, make sure that you have black dye on hand. Then, detecting the presence of a mink and permanently solving the problem, is difficult, but can be done.